From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7E4BEC169C4 for ; Wed, 6 Feb 2019 20:20:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 42D5F20823 for ; Wed, 6 Feb 2019 20:20:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Ab/ZKKur" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726266AbfBFUUZ (ORCPT ); Wed, 6 Feb 2019 15:20:25 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:48856 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725956AbfBFUUZ (ORCPT ); Wed, 6 Feb 2019 15:20:25 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=zxiuA+kMki/UhwSsnRN7805PLjtsIi6PGZFOiQ1YwQk=; b=Ab/ZKKurlrlfBf27eXyZXOAoc vMRey/USNDaTEnIgHG3mGDD3ZLLM1aisiG7e0shzKeua0xOugZ2EixdhKk8B/pBQs/aw+NSJl72+5 WMkK95M7MEOG8rcRdlRibITDjzsg7gYTfhH7d/kL6LnJUluCZ+vN+M8uKloKFKAm911wua3K4IyY3 53oawd2oTBqnpQUtZm7AniaJvkc/6VKZ2z8miEukueTSg6krxGKQwIAjLR9/OjAHNFuYR9jAAjSIv YJJS0o8Mt+ikxTAoYusqDbJtLVPBy3+FsI3TMamjD6SZsPHbOoiOqU0ENz7ItusFaSmT4pmdeN7qx ME+59Vxyw==; Received: from willy by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1grTgD-0003Sc-As; Wed, 06 Feb 2019 20:20:21 +0000 Date: Wed, 6 Feb 2019 12:20:21 -0800 From: Matthew Wilcox To: Doug Ledford Cc: Christopher Lameter , Jason Gunthorpe , Jan Kara , Ira Weiny , lsf-pc@lists.linux-foundation.org, linux-rdma@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, John Hubbard , Jerome Glisse , Dan Williams , Dave Chinner , Michal Hocko Subject: Re: [LSF/MM TOPIC] Discuss least bad options for resolving longterm-GUP usage by RDMA Message-ID: <20190206202021.GQ21860@bombadil.infradead.org> References: <20190205175059.GB21617@iweiny-DESK2.sc.intel.com> <20190206095000.GA12006@quack2.suse.cz> <20190206173114.GB12227@ziepe.ca> <20190206175233.GN21860@bombadil.infradead.org> <47820c4d696aee41225854071ec73373a273fd4a.camel@redhat.com> <01000168c43d594c-7979fcf8-b9c1-4bda-b29a-500efe001d66-000000@email.amazonses.com> <20190206194055.GP21860@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 06, 2019 at 03:16:02PM -0500, Doug Ledford wrote: > On Wed, 2019-02-06 at 11:40 -0800, Matthew Wilcox wrote: > > On Wed, Feb 06, 2019 at 07:16:21PM +0000, Christopher Lameter wrote: > > > > > > though? If we only allow this use case then we may not have to worry about > > > long term GUP because DAX mapped files will stay in the physical location > > > regardless. > > > > ... except for truncate. And now that I think about it, there was a > > desire to support hot-unplug which also needed revoke. > > We already support hot unplug of RDMA devices. But it is extreme. How > does hot unplug deal with a program running from the device (something > that would have returned ETXTBSY)? Not hot-unplugging the RDMA device but hot-unplugging an NV-DIMM. It's straightforward to migrate text pages from one DIMM to another; you remove the PTEs from the CPU's page tables, copy the data over and pagefaults put the new PTEs in place. We don't have a way to do similar things to an RDMA device, do we?